# Electromagnetic induction-help with a problem

endeavor
"A metal rod 20 cm long moves in a straight line at a speed of 4.0 m/s with its length parallel to a uniform magnetic field of 1.2 T. Find the resulting potential difference between the ends of the rod."

I don't know how to solve this...

## Answers and Replies

Gold Member
Did you learn the induced potential equation? (Blv)
also, I'm not sure that I understand the case, the length of the rod is moving through the field and the field is going from one end of the rod to the other? In that case there would be no induction, for there to be induction there has to be a field that makes a right angle with the length of the rod.

endeavor
I mainly learned about loops of wire, not rods...what exactly is a rod? I thought that it's a cylinder...

Oh, is this refering to the metal rod that moves on a metal frame so that the area inside the loop of the frame changes? My book has one example of that, and the equation is emf = -BLv.

If that's the case, then since the flux doesn't change because the field is parallel, then the induced emf is 0.

Staff Emeritus
Gold Member
endeavor said:
I mainly learned about loops of wire, not rods...what exactly is a rod? I thought that it's a cylinder...

Oh, is this refering to the metal rod that moves on a metal frame so that the area inside the loop of the frame changes? My book has one example of that, and the equation is emf = -BLv.

If that's the case, then since the flux doesn't change because the field is parallel, then the induced emf is 0.
A rod is basically a thin cylinder, that is a cylinder with a length but no radius. This page may be useful for you... http://www.iop.org/Our_Activities/Schools_and_Colleges/Teaching_Resources/Teaching%20Advanced%20Physics/Fields/Electromagnetism/page_4817.html [Broken]
Your equation is correct by the way but your conclusions are not Last edited by a moderator:
endeavor
Hootenanny said:
Your equation is correct by the way but your conclusions are not I found out that the answer is 0... but since my conclusions are wrong, I don't know how this answer has been derived. Staff Emeritus
I found out that the answer is 0... but since my conclusions are wrong, I don't know how this answer has been derived. Ahh my apologies, your conclusion is correct I didn't see the 'parallel' bit Ahh my apologies, your conclusion is correct I didn't see the 'parallel' bit 